1. Field of the Invention
The present invention relates to a relay station, a base station, and a communication system utilizing radio communication. The present invention is particularly suitable for a relay station, a base station, and radio communication system when the relay station is introduced to a radio communication system specified, for example, by IEEE802.16.
2. Description of the Related Art
A radio communication system to realize communication via a radio communication link is now spreading on a world-wide scale as a representative system of the WCDMA and CDMA 2000. In this radio communication system, a plurality of base stations are provided in a service area respectively and a mobile station makes communication with the other communication devices (communication terminals) via any of the base stations. Moreover, in such a system, a service area formed by a base station is overlapped with another service area formed by an adjacent base station. Therefore the communication can be maintained by a handover process even though radio environment of the communication gets worse.
Moreover, as a radio communication system, the technologies, for example, code division multiplex, time division multiplex, frequency multiplex and orthogonal frequency division multiple access (ODFM or OFDMA) are generally employed and thereby a plurality of mobile stations can be connected to a base station simultaneously.
However, when a mobile station is close to the boundary of a service area formed by a base station, even though within the service area, high-speed communication becomes difficult for the mobile station because the radio communication environment is deteriorated.
Therefore, a communication system has been proposed, in which a relay station is provided within the service area of a base station to realize radio communications between a mobile station and the base station via the relay station.
Particularly, introduction of such a relay station (RS) is now discussed by the task group of 802.16j.
Matters regarding IEEE802.16 are disclosed, for example, in the IEEE Std802.16TM-2004 and the IEEE Std802.16eTM-2005.